Method and apparatus for opening tubes of flexible material

ABSTRACT

A method and apparatus for spreading open the ends of bag tube blanks in a bag forming machine wherein a pair of opposing suction cups, one on each side of the path of movement of the blanks are moved in a circular path with respect to the machine frame. At the same time the suction cups are counter rotated at the same angular speed but in directions opposite to their movement in the circular path whereby the suction cup faces maintain constant their angular relationship with respect to the machine frame. The paths of movement of the cups are selected to provide concurrent tangential passage of the cups with the two walls of the bag blank and a suction pressure is applied to the cups when they are in contact with the blank. The blank is opened by action of the suction pressure as the cups move away from each other.

[ Sept. 10, 1974 United States Patent 1191 Hollis [54] METHOD AND APPARATUS FOR OPENING Primary Examiner Donald R. Schran TUBES OF FLEXIBLE MATERIAL Attorney, Agent, or FirmR. S. Sanborn; W. T.

Zielinski; W. A. Aguele [75] Inventor: Clinton R. Hollis, Camden, Ark.

[73] Assignee: International Paper Company, New

York, NY.

f o M e m fi m em r Oa S mk Filed! J 1972 A method and apparatus for spreading open the ends [211 App! Nu2 267,361 of bag tube blanks in abag forming machine wherein a pair of opposing suction cups, 0 the path of movement of the blan circular path with respect to the mac [2%] 936%;35353 the Same time the Suction cups are counter rotated at h d i 35 3O 21 the same angular speed but in directions opposite to 0 4 their movement in the circular path whereby the suction cup faces maintain constant their angular relationship with respect to the machine frame. The paths [56] References cued of movement of the cups are selected to provide con- UNlTED STATES PATENTS current tangential passage of the cups with the two 2 707,421 Rawe 93/28 walls of the bag blank and a suction pressure is applied to the cups when they are in contact with the FOREIGN PATENTS OR APPLICATIONS blank. The blank is opened by action Of the suction pressure as the cups move away from each other.

3 Claims, 4 Drawing Figures VACUUM 4? souRcE CAM OPERATED PNEUMATlC VALVE Pmamsusm 3.884.287

SHEET 20? 2 i Q. l V

METHOD AND APPARATUS FOR OPENING TUBES OF FLEXIBLE MATERIAL BACKGROUND OF THE INVENTION This invention pertains to a method and apparatus for spreading open the walls of an essentially flat tube of flexible material and more particularly relates to a method and apparatus for spreading open the walls of paper tube blanks in a bag forming machine There are various known embodiments of bag forming machines for forming bags from tube stock of flexible material such as kraft paper. Usually, the bag blanks are separately made by a tubing machine which provides a continuous tube having a longitudinal seam prepared from sheet stock and cuts the tube to a series of blanks of predetermined length suitable for the bag to be formed. These blanks are then processed through a bag forming machine for forming at least one sealed end.

The machine is adapted to process a large volume of bag blanks. Thus, the blanks are continuously fed into the machine which includes means for transporting the bag blanks in series manner through several stations where the various operations for forming the bag bottom are automatically performed. The blank is first scored lightly to provide the fold lines necessary for forming the bottom while the tube is in an essentially flat condition in one plane. The bottom end of the tube is then partially folded along a line transverse to the tube while the two walls of the ends still remain adjacent each other. These walls are then spread open and folded into the plane of the blank to provide exposed inner surfaces of the end portion. A suitable cement is then roller applied to the exposed surfaces and additional folding is performed to provide the necessary overlying layers of the tube end to form the bottom of the bag.

A typical prior art bag forming machine is described in greater detail in U.S. Pat. No. 2,707,421 to M. Rawe. As illustrated in FIG. of that patent the tube end is first partially opened by suction devices 3; the spreader finger 4 enters between the partially opened walls and opens them further. Then, the bow shaped forming members 5 enter the partially opened tube end to fold the tube walls into the plane of the tube blank.

This type of tube end spreading mechanism is quite common in prior art bag forming machines. In some machines the spreader finger is omitted.

A serious problem associated with such prior art spreading mechanisms is that the suction devices occasionally do not pre-open the tube ends sufficiently. In such instances, the spreading finger or the bow shaped forming members crush the end of the bag blank whereby a malformed bag is produced. Since the suction devices move around a circular path their faces are jointly parallel with the walls of the bag tube at only one point in their paths of motion. This is at their point of contact with the tube walls. Thus, as the suction devices approach the tube walls they form a distinct angle which decreases until contact is made and then they assume a departing angular relationship as they rotate away from the tube walls. As a result of these dynamics a firm vacuum grasp is occasionally not made and an objectionally high number of rejected bags is produced. Also, these dynamics operate as a constraint on the usefulness of the machine since when bag sizes are made which depart from the optimum or nominal design size upon which the geometry of the spreading mechanism is predicated, the rejection rate if further increased.

Several attempts have been made to solve this problem among which is increasing the radius of the arc of movement of the suction devices so that they contact the tube end walls with a distinct interference or force against each other, to enhance the likelihood of a firm vacuum grasp. This results in premature wear of the forward corner of the vacuum cups having the adverse effect of increasing the down-time of the machine. Other attempts include reducing the size of the vacuum cup in an effort to alleviate the corner wear problem while increasing the vacuum pressure. It was found that this did not sufficiently increase the effectiveness of the vacuum devices to substantially reduce the objectionable rejection rate.

The invention as herein described solves the aforementioned problems by providing a far superior dynamic operation of the spreading mechanism wherein the suction cups approach each other while maintaining their faces in essentially constant angular relationship, perform their spreading function, and move away from each other with their faces in essentially unchanged angular relationship. The invention has been found so effective that when making certain select sizes of bags from relatively heavy stock it is possible to omit one of the rotating suction devices and replace it merely by a wall against which the bag tube end may rest while it is partially opened by the remaining suction device. SUMMARY One aspect of the present invention resides in a method of spreading open the walls of a tube of flexible material, including first and second walls essentially facing each other wherein the tube is in motion in a predetermined direction, including the steps of; contacting the first wall of the tube with the suction face of a suction cup wherein the face is essentially parallel to the walls of the tube, and moving the suction cup at least in part during the contacting step in a direction having at least a vector component parallel to said predetermined direction of movement of the tube. The method includes the further steps of; applying a suction pressure to the suction cup at least in part during the contacting step, and moving the suction cup in a direction away from the first wall while applying the suction pressure and while maintaining the suction cup face essentially parallel to the walls of the tube, thereby moving the first wall in a direction away from the second wall by action of the suction pressure.

In a preferred version of the method of the invention a pair of opposing suction cups are employed with the steps including; contacting the walls of the tube with the respective suction faces of the cups, one on each side of the tube, wherein the faces of the cups are essentially parallel, and moving the suction cups at least in part during the contacting step in a direction having at least a vector component parallel to the predetermined direction of movement of the tube. This version of the method includes the further steps of; applying a suction pressure to the suction cups at least in part dur ing the contacting step, and moving the suction cups away from one another while applying the suction pressure and while maintaining the faces thereof in essentially parallel relationship so that the walls of the tube are caused to be moved away from each other by action of the suction thereby opening the tube in the vicinity of the suction cups.

Yet another aspect of the invention resides in an apparatus combination contemplated for use in connection with a bag forming machine wherein the machine includes a frame, means in the frame for folding the ends of the bag tube blank to provide a plurality of overlying layers thereof while the end of the tube is in motion, means in the machine frame for moving the end of the tube into the folding means in a determined direction to perform the folding, and means operatively coupled with the folding means for securing the overlying layers to form the bag bottom. The preferred apparatus combination in accordance with the present invention is operatively coupled with the folding means and is for opening the end of the tube while the end is in motion in the aforementioned direction prior to completion of the folding thereof. This apparatus combination includes; a pair of suction cups, a first support member, means for rotating one of the suction cups at a predetermined angular velocity about a first axis which is positioned in the first support member, and means for rotating the support member at an angular velocity substantially equal to but opposite in direction to the predetermined angular velocity about an axis second which is positioned in the machine frame essentially parallel to the first axis and positioned to provide an essentially tangential passage of the suction face of the first cup with a first wall of the tube end in substantially the same direction as the predetermined direction of movement of the tube end.

The apparatus further includes; a second support member, means for rotating the second suction cup about an axis third which is positioned in the second support member, means for rotating the second support member in synchronism with the first support member at an angular velocity substantially equal to but opposite in direction to the rotation of the second suction cup about the axis third, the rotation of the second support member being about an axis fourth which is positioned in the machine frame essentially parallel to the axis third and positioned to provide an essentially tangential passage of the suction face of the second cup with a second wall of the tube end in the vicinity of, substantially in the same direction and concurrent with, the tangential passage of the first suction cup. The apparatus further includes; means for applying a suction pressure to the first and second suction cups at least in part during the aforementioned tangential passages thereof with the walls of the tube end.

As a consequence of the double rotation of the suction cups, more specifically including the rotation of the cups with respect to the support members, the cup faces do not change their angular relationship with themselves or with the tube end walls throughout their respective paths of motion. Thus, the suction cups can be initially set in parallel relationship with the tube wall path and they will maintain this relationship throughout their respective motions. This results in greatly improved vacuum contact with the tube walls.

Furthermore, there is little or no transverse movement of the suction cups with respect to the tube walls while they are in contact therewith resulting in substantially less wear of the cup faces.

A further advantage of the invention resides in doing away with the necessity of employing the conventional rotating vacuum couplings associated with the prior art tube end spreading devices for providing a vacuum through the drive shafts of the vacuum cups. Since the vacuum cups of the present invention do not rotate with respect to the machine frame, a suction source can be directly coupled to the cups. This further increases the reliability of the machine. Another advantage of the invention is that bag tubes having minor inside sticking problems associated with the longitudinal glued joint can be effectively opened. Also, it can be understood that the invention results in a much wider pre-opening of the bag tube than heretofore obtained.

In view of the foregoing it is an object of the present invention to provide improved methods and apparatus for spreading open the walls of a tube of flexible mate rial.

It is another object of the invention to provide a method and apparatus of improved effectiveness for spreading open the walls of a tube of paper-like material in connection with bag making machines.

It is another object of the invention to provide method and apparatus improvements which reduce the rejection rate of bags made by a bag making machine.

It is another object of the invention to provide an improved method and apparatus for the vacuum opening of the walls of a bag tube blank enabling the use of vacuum cups of enlarged face area.

It is yet another object of the present invention to provide an improved method and apparatus for the vacuum opening of the walls of a bag tube blank in a bag making machine for reducing the wear of the vacuum cups and reducing the downtime of the machine.

It is another object of the invention to provide improved apparatus for the vacuum opening of a bag tube enabling the use of a more simplified vacuum coupling system.

It is yet a further object of the invention to provide an improved apparatus for the vacuum opening of a bag tube blank for use in a bag making machine extending the flexibility of usefulness of the machine.

These and other objects, advantages and features of the invention, will be more fully understood by referring to the following descriptions and claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary, perspective view, partly in section, of a portion of the inlet end of a bag making machine illustrating the prior art apparatus for opening the end of a bag tube.

FIG. 2 is a cross-sectional view taken in the direction 2 2 of FIG. 1 wherein the apparatus for opening the bag tube ends is replaced by improved apparatus illustrating features of the present invention.

FIG. 3 is an end view, partly in section, of FIG. 2 in the direction 3 3, illustrating in greater detail the preferred apparatus of the invention including the several axes of rotation and drive means therefore.

FIG. 4 is a plan view taken in the direction 4 4 of FIG. 3 illustrating in still further detail the drive mechanism for the tube suction cups.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, which partly illustrates the inlet portion of a bag making machine, essentially fiat bag tube blanks 12 are sequentially introduced into the machine by conventional feeding apparatus not shown. It will be understood that as used herein the term essentially flat is intended to describe the relaxed shape assumed by a bag tube of generally flexible material such as kraft paper. Thus, the walls of the tube will tend to rest adjacent each other under the influence of gravity while the ends of the tube do not necessarily have a distinct longitudinal fold line.

The tube blanks are transported through the bag making machine by suitable conveyor means such as endless belts 13, 14 which incorporate suitable grasping means for holding the tube blanks.

A stationary machine frame 15 is illustrated which includes a suitable bed upon which the endless belts 13, 14 move. A stationary guide bar 16 is provided positioned essentially transverse to the machine direction beneath which the end of the bag tubes are transported. Adjacent the bar 16 is a cam plate 17 having a gradually inclining curved surface which rises to a perpendicular relationship with the plane of travel of the bag tubes. Thus, as the bag tubes pass over the cam plate 17 the tube end is folded along a line transverse to the tube and essentially perpendicular to the plane of the tube. Therefore, an upstanding end 19, of the tube, is formed.

For brevity, the conventional scoring drums have been omitted from FIG. 1. These provide the several score lines required to define the various fold lines for forming the overlying layers of the tube end to serve as the bag bottom. The scoring drums are generally positioned in the machine ahead of the cam plate 17 so that the scoring is performed prior to folding the upstanding end 19.

The fold formed by the cam 17 is not exceptionally sharp so that a small radius is left at the fold line. Thus, the upstanding end 19 is of somewhat relaxed condition depending upon the weight of paper stock used and defines a plane of somewhat variable width parallel to the machine direction. The plane is somewhat thicker at the end of the tube than it is in the central region where the walls tend to rest adjacent each other.

Several further operations, not illustrated, are required to form the bag. The upstanding end is first spread open then flattened back into the plane of the tube leaving exposed the inner surfaces of the tube end. Then, adhesive is applied to the exposed inner surfaces and they are again folded to provide secured overlying layers. Appropriate apparatus for performing these functions is illustrated in the aforementioned patent US. Pat. No. 2,707,421.

As illustrated in FIG. 1, the prior art method of preopening the bag tube end employs a pair of suction cups rigidly rotated by a pair of driven shafts 21, 22 which are equidistantly disposed on either side of the path of passage of the upstanding tube end 19 and parallel therewith. For supporting the shafts 21, 22 the machine frame includes an overhead frame member 23 having downwardly depending bearing bosses 24, 25. The bosses include suitable bearings in which the shafts 21, 22 rotate. Also, the bosses 24, 25 respectively include stationary arms 26, 27 which depend from the lower ends thereof. Mounted for rotation about horizontal axes in the arms 26, 27 are a pair of shafts which respectively include bevel gears 28, 29. These respectively engage bevel gears 30, 31 keyed to the shafts 21, 22. The shafts of the bevel gears 28, 29 have fixed to their respective ends bow-shaped forming members 32, 33 for concurrent rotation thereof in essentially vertical planes. Non-rotatably connected to the lower ends of the shafts 21, 22 are a pair of opposing suction cups.

The shafts 21, 22 are driven in synchronism at equal angular speed and in equal opposite directions such that the suction cups associated therewith are opposite each other when a bag blank is present between the shafts 21, 22. Thus, the suction cups make a tangential passage along the upstanding end 19 while both cups are moving in essentially the same direction as the tube end. The tangential passage can be arranged so that there is some interference i.e., the cups will concurrently apply some force on each other as the tube end is trapped between them. Or, the tangential passage can be adjusted to have some clearance so that suction cups are not subjected to any mechanical pressure as they jointly contact the bag tube.

A cam operated pneumatic valve 40 is schematically illustrated mechanically coupled with the drive means for driving the shafts 21, 22. A vacuum source 41 is connected with the valve 40. The shafts 21, 22 are hollow thereby providing a passageway communicating with the rotating suction cups. The upper ends of the shafts 21, 22 include appropriate rotating vacuum couplings, not shown, and a pneumatic tube connection, not shown, connected with the pneumatic valve 40 for receiving a vacuum pressure. The cam operated pneumatic valve is arranged to apply a vacuum to the shafts 21, 22 the moment the suction cups approach the tube end walls. The vacuum pressure is kept on for a short period of time as the suction cups pull away from each other partially opening the tube end. The vacuum is then immediately shut off to prevent tearing of the tube walls. This is required since the circular path of motion of the suction cup faces provides a velocity thereof which is in agreement with the velocity of the tube end only at the point of contact.

The bow-shaped forming members 32, 33 are axially offset slightly so that the ends thereof are one behind the other in the machine direction. These ends immediately enter the partially opened tube end spreading it further to a fully opened condition into the plane of the tube exposing the inner surfaces thereof.

A major disadvantage of this prior art method and apparatus for opening the tube end arises from the fact that the faces of the suction cups are constantly changing their angular relationship whereby they are parallel with each other at only one point in their paths of motion, namely, the point of contact with the tube end. As a result, it has been necessary to adjust their respective radius arms of rotation such that their tangential passage is one involving interference, or mechanical pressure with each other and the tube end, in order to minimize the number of improperly formed bags. As indi-. cated above this measure has not proved entirely satisfactory.

Referring now to FIG. 2 which is a cross-sectional view along the lines 2 2 of FIG. 1 wherein the tube end opening device is modified to include features of the present invention, the depending stationary boss 25 is lengthened in a downward direction and includes an opening 45 to accompany the bevel gear 29. A solid shaft 52 is used in place of the hollow shaft 22 and has suitably keyed to its upper end a driven gear 53. A suction cup 54 is shown to which is fitted a vacuum line 55.

Referring now jointly to FIGS. 3 and 4, several axes of rotation are identified. A first axis of rotation is occupied by a shaft 56 to which is fixed the suction cup 54. The second axis of rotation is occupied by the shaft 52. The third axis of rotation is occupied by a shaft 57 the lower end of which is fixed to a suction cup 58. The fourth axis of rotation is occupied by a shaft 59 which replaces the hollow shaft 21.

The gear 53 is appropriately fixed or keyed to the shaft 52 and engages a gear 60 having an equal number of teeth and which is fixed to the shaft 59. Suitable means are provided, not shown, for driving the gear 53 by the common machine drive mechanism which drives the endless belt 13, 14. Thus, the movement of the gears 53, 60 will maintain their established relationship with respect to the movement of the bag tubes notwithstanding variations of speed of the machine drive mechanism. The same common drive is used to operate the cam, now shown, associated with the cam operated pneumatic valve 40.

The shaft 52 is rotateably mounted in the overhead frame 23 with bearings 63, 64. The lower bearing 64 is directly fitted into a counterboard portion of the boss 25. The upper bearing 63, is fitted in a bearing retaining ring 65 which is, in turn, fitted into a mating counter bore in the overhead frame member.

A second counter bore is provided in the lower surface of the boss 25 into which is snugly fitted the hub end of a gear 68. The counter bore is arranged concentric with the axis of the shaft 52 so that the pitch diameter of the gear 68 is generally concentric with the shaft 52. A set screw 69 is employed to secure the gear 68 in non-rotatable relationship with the boss 25. A support member 70 is clamped to the lower end of the shaft 52 with a clamping screw 71. A slot is provided in the wall of the support member 70 to obtain the desired clamping action. An idler gear 73 is provided which is rotateably mounted to the support member for engagement with the stationary gear 68. The idler, in turn, is engaged with a gear 74 which is rotateably mounted in the support member 70. More specifically, the gear 74 is clamped to the shaft 56 with a gear clamp and screw 75. An extended hub portion of the gear 74 is provided over the end portion of which the gear clamp 75 is fitted. Also, this hub is fitted in bearings 76, 77 which are, in turn, fitted in the support member 70 to permit rotation of the shaft 56 with respect to the support member. The suction cup 54 is fixed to the lower end of the shaft 56.

As the gear 53 is driven by the machine common drive mechanism it rotates the shaft 52 which carries with it the support member 70 so that the first axis of rotation occupied by the shaft 56 is caused to rotate about the shaft 52 in a circular path. As shown in FIG. 4, the direction of rotation of the gear 53 and the sup port member 70 illustrated clockwise. The idler gear 73 is caused to rotate by the stationary gear 68 as its pivotal axis is carried around the gear 68 by the support member 70. The idler 73, in turn, drives the gear 74 in a counter clockwise direction, resulting in a counter clockwise movement of the shaft 56 with respect to its axis. The gears 68 and 74 have the same number of teeth so that for each clockwise revolution of the support member 70 the shaft 56 makes counter clockwise revolution. Thus, the angular velocity of the shaft 56 about the axis of the shaft 52 is equal to but opposite in direction to the angular velocity of the suction cup 54 with respect to the shaft 56.

It is seen that the suction cup 54 moves in a circular path while maintaining constant the angular relationship of the plane of its face with respect to the machine frame.

The suction cup 58 is driven by an identical but mirror image mechanism of that used for driving the cup 54. The gears 53, and the center distances between the shafts 52, 56 and 57, 59 are selected to provide a peripheral speed of the faces of the cups 54, 58 approximately equal to the speed of movement of the tube end at the point of tangent intersection with the tube end. It can be understood that due to the improved performance of the suction cups wide tolerances of this speed are found acceptable.

Also, the cups 54 and 58 are initially set up parallel with each other and with the path of movement of the tube ends by adjustments of the clamp and screw 75. Likewise, reasonably wide tolerances of this angular relationship are acceptable since, once established, the angular relationships of the cups remain unchanged as they are moved through their respective paths. I have found that an angular tolerance from parallel of 10 to be quite acceptable.

The cam operated pneumatic valve 40 is preferably arranged to simultaneously apply a vacuum pressure to the suction cups approximately 5 of their respective rotation about the shafts 52, 59 prior to being opposite each other and the vacuum pressure is kept on for a total angle of about 35 of said rotation. It can be understood that the vacuum pressure can be kept on for a longer interval than it could with the prior art opening mechanism. Also, the present invention makes it possible to employ suction cups of much larger diameter thereby further improving their operation.

It is preferred that the shafts 52, 56, 57, and 59 be arranged generally perpendicular to the bed of the machine so that the cups 54, 58 move generally in the same direction as the tube ends at the point of their tangential passage. However, I have found that the present invention makes possible very wide variations from this preferred design. Indeed, acceptable performance is obtained if the movement of the suction cups merely has a vector component in the same direction as the tube end direction of movement when making the tangential passage. Also, wide tolerances of the nature of this tangential passage can be absorbed. It can be a passage of the cups in which only brushing contact is made with the tube walls or one which involves a substantial pressure between the two cups with the tube walls therebetween. Thus, as used herein, the term tangential passage is intended to embrace a family of arcs of movement of the cups which come near the tube end walls or which intersect with them.

In a specific example the gears 68 and 74 were selected having a pitch diameter of 2% inches. A pitch diameter of 1% inches was chosen for the idler gear 73 and it was positioned to provide a center distance, R between the shafts 52 and 56 of 2 /2 inches. The radius of movement of the face of the cup with respect to the shaft 56, R was chosen as 2% inches. The cups were placed to provide approximately a Iine-to-line condition thereof without a bag tube present at the nearest point at their tangential passage.

It can be seen by those skilled in the art that the path of movement of the suction cup 54 with respect to the machine frame is a circle of radius R with its axis displaced toward the bag tube end by a distance R, from the axis of the shaft 52. Thus, the preferred angular speed of the gear 53 can be easily calculated to provide a peripheral speed at a radius R approximately equal to the speed of the bag tube end.

By employing the tube end opening device hereinabove described it became possible to substantially increase the speed of the bag forming machine while lowering to substantially zero the rate of malformed bags attributable to improper end opening.

While the invention has been described with a certain degree of particularity it can, nevertheless be seen, by the examples hereinabove set forth, that many variations and modifications of the invention can be made without departing from the true spirit and scope thereof.

I claim:

1. In connection with a process for forming a closed bottom of a bag formed from an essentially flat tube of flexible material including the steps of, folding the end of said tube to provide a plurality of overlying layers of said tube end, and securing said overlying layers to form said bag bottom, wherein said tube end is in motion in a predetermined direction at least in part during said folding step; a method for opening said tube end prior to said folding step comprising the steps of:

a. rotating a first suction cup about a first axis;

b. rotating said first axis about an axis second which is essentially parallel to said first axis, said rotating (b) being at an angular speed essentially equal to said rotating (a) but opposite in direction thereto;

wherein said axes are positioned and the directions of said rotations are selected to provide essentially tangential passage of the face of said cup with a first wall of said tube end with said cup moving in essentially the same direction as said tube end during said tangential passage and with said face of said suction cup essentially parallel to said wall of said tube end at least in part during said tangential passage; and c. applying a suction pressure to said suction cup at least in part during said tangential passage thereby tending to spread open said tube end by action of said suction pressure. 2. The method of claim 1 including the further steps of:

d. rotating a second suction cup about an axis third;

e. rotating said axis third about an axis fourth which is essentially parallel to said axis third, said rotating (e) being at an angular speed essentially equal to said rotating (d) but opposite in direction thereto;

wherein said axes third and fourth are positioned and the directions of said rotations (d), (e) are selected to provide essentially tangential passage of the face of said second cup with the second wall of said tube end in the vicinity of and substantially concurrent with the tangential passage of said first cup face with said first wall wherein said axes are positioned and said directions of rotation are selected to provide movement of said second cup in essentially the same direction as said tube end during said tangential passages with said face of said second suction cup essentially parallel to said second wall of said tube end at least in part during said tangential passages; and

f. applying a suction pressure to said second suction cup at least in part during said tangential passages.

3. The method of claim 2 wherein said rotating steps (b) and (e) are performed in a manner such that said axes second and fourth are essentially parallel and positioned such that the path of movement of said tube end passes equidistantly from said axes second and fourth and is essentially perpendicular to the plane joining said axes second and fourth. 

1. In connection with a process for forming a closed bottom of a bag formed from an essentially flat tube of flexible material including the steps of, folding the end of said tube to provide a plurality of overlying layers of said tube end, and securing said overlying layers to form said bag bottom, wherein said tube end is in motion in a predetermined direction at least in part during said folding step; a method for opening said tube end prior to said folding step comprising the steps of: a. rotating a first suction cup about a first axis; b. rotating said first axis about an axis second which is essentially parallel to said first axis, said rotating (b) being at an angular speed essentially equal to said rotating (a) but opposite in direction thereto; wherein said axes are positioned and the directions of said rotations are selected to provide essentially tangential passage of the face of said cup with a first wall of said tube end with said cup moving in essentially the same direction as said tube end during said tangential passage and with said face of said suction cup essentially parallel to said wall of said tube end at least in part during said tangential passage; and c. applying a suction pressure to said suction cup at least in part during said tangential passage thereby tending to spread open said tube end by action of said suction pressure.
 2. The method of claim 1 including the further steps of: d. rotating a second suction cup about an axis third; e. rotating said axis third about an axis fourth which is essentially parallel to said axis third, said rotating (e) being at an angular speed essentially equal to said rotating (d) but opposite in direction thereto; wherein said axes third and fourth are positioned and the directions of said rotations (d), (e) are selected to provide essentially tangential passage of the face of said second cup with the second wall of said tube end in the vicinity of and substantially concurrent with the tangential passage of said first cup face with said first wall wherein said axes are positioned and said directions of rotation are selected to provide movement of said second cup in essentially the same direction as said tube end during said tangential passages with said face of said second suCtion cup essentially parallel to said second wall of said tube end at least in part during said tangential passages; and f. applying a suction pressure to said second suction cup at least in part during said tangential passages.
 3. The method of claim 2 wherein said rotating steps (b) and (e) are performed in a manner such that said axes second and fourth are essentially parallel and positioned such that the path of movement of said tube end passes equidistantly from said axes second and fourth and is essentially perpendicular to the plane joining said axes second and fourth. 